[receiver/awsfirehose] Refactor to use pdata unmarshaler interfaces

[axw]

Description

Refactor unmarshallers to fit into the encoding framework.

The internal unmarshallers now implement plog.Unmarshaler and pmetric.Unmarshaler. This will enable us to use encoding extensions in a followup, and will enable us to extract the unmarshallers later as encoding extensions.

As a result of the interface change, the unmarshallers now unmarshal a single record at a time, which means we cannot merge resources/metrics as we go, and only within each record. This impacts performance, so to offset that we implement various optimisations:

• Use json-iterator for decoding JSON
• Use klauspost/compress for decompressing gzip
• Pool gzip readers
• Remove pointer type from cwMetricValue to avoid allocation
• Don't read the whole request body into memory
• Reuse buffer for decoding base64; decode as we go

There are more optimisations we can make to reduce memory allocations, e.g. avoid reflection when decoding JSON.

There's a fix for a subtle bug in the cwmetrics unmarshaller where the unit of a metric was not considered part of its identity, and so two metrics that differed only by unit would be merged.

Link to tracking issue

Preparation for #37113

Testing

• Added tests for consuming requests containing multiple records.
• Added benchmarks for the full request/response flow, for cwlogs and cwmetrics record types. There's an increase in memory usage for cwmetrics unmarshalling, and decrease for cwlogs unmarshalling. CPU usage is better across the board.

goos: linux
goarch: amd64
pkg: github.com/open-telemetry/opentelemetry-collector-contrib/receiver/awsfirehosereceiver
cpu: AMD Ryzen 7 PRO 5850U with Radeon Graphics     
                                                              │ /tmp/old.txt  │            /tmp/new.txt             │
                                                              │    sec/op     │    sec/op     vs base               │
LogsConsumer_cwlogs/10resources_10records_1logs-16              142.03µ ±  8%   75.85µ ± 16%  -46.60% (p=0.002 n=6)
LogsConsumer_cwlogs/10resources_10records_10logs-16              413.1µ ±  5%   208.0µ ± 23%  -49.65% (p=0.002 n=6)
LogsConsumer_cwlogs/10resources_100records_1logs-16             1435.8µ ±  8%   728.0µ ± 11%  -49.30% (p=0.002 n=6)
LogsConsumer_cwlogs/10resources_100records_10logs-16             4.200m ±  2%   1.875m ±  4%  -55.34% (p=0.002 n=6)
MetricsConsumer_cwmetrics/10resources_10records_1metrics-16     104.30µ ± 16%   70.26µ ± 12%  -32.64% (p=0.002 n=6)
MetricsConsumer_cwmetrics/10resources_10records_10metrics-16     821.7µ ±  7%   505.5µ ±  5%  -38.48% (p=0.002 n=6)
MetricsConsumer_cwmetrics/10resources_100records_1metrics-16     780.2µ ±  5%   647.0µ ±  8%  -17.07% (p=0.002 n=6)
MetricsConsumer_cwmetrics/10resources_100records_10metrics-16    7.823m ±  5%   5.297m ± 11%  -32.29% (p=0.002 n=6)
geomean                                                          809.9µ         475.7µ        -41.26%

                                                              │ /tmp/old.txt  │             /tmp/new.txt             │
                                                              │     B/op      │     B/op      vs base                │
LogsConsumer_cwlogs/10resources_10records_1logs-16              437.78Ki ± 0%   61.70Ki ± 1%   -85.91% (p=0.002 n=6)
LogsConsumer_cwlogs/10resources_10records_10logs-16              533.7Ki ± 0%   124.9Ki ± 2%   -76.60% (p=0.002 n=6)
LogsConsumer_cwlogs/10resources_100records_1logs-16             4319.1Ki ± 0%   550.1Ki ± 0%   -87.26% (p=0.002 n=6)
LogsConsumer_cwlogs/10resources_100records_10logs-16             5.167Mi ± 0%   1.172Mi ± 1%   -77.31% (p=0.002 n=6)
MetricsConsumer_cwmetrics/10resources_10records_1metrics-16      47.88Ki ± 5%   83.71Ki ± 0%   +74.84% (p=0.002 n=6)
MetricsConsumer_cwmetrics/10resources_10records_10metrics-16     390.0Ki ± 1%   415.4Ki ± 1%    +6.51% (p=0.002 n=6)
MetricsConsumer_cwmetrics/10resources_100records_1metrics-16     358.9Ki ± 0%   772.9Ki ± 0%  +115.37% (p=0.002 n=6)
MetricsConsumer_cwmetrics/10resources_100records_10metrics-16    3.730Mi ± 0%   3.962Mi ± 0%    +6.23% (p=0.002 n=6)
geomean                                                          779.7Ki        391.8Ki        -49.76%

                                                              │ /tmp/old.txt │            /tmp/new.txt            │
                                                              │  allocs/op   │  allocs/op   vs base               │
LogsConsumer_cwlogs/10resources_10records_1logs-16                406.0 ± 2%    348.0 ± 2%  -14.29% (p=0.002 n=6)
LogsConsumer_cwlogs/10resources_10records_10logs-16              2.025k ± 0%   1.971k ± 1%   -2.64% (p=0.002 n=6)
LogsConsumer_cwlogs/10resources_100records_1logs-16              2.922k ± 0%   3.094k ± 0%   +5.89% (p=0.002 n=6)
LogsConsumer_cwlogs/10resources_100records_10logs-16             18.46k ± 0%   19.46k ± 1%   +5.45% (p=0.002 n=6)
MetricsConsumer_cwmetrics/10resources_10records_1metrics-16       548.5 ± 8%    653.0 ± 0%  +19.05% (p=0.002 n=6)
MetricsConsumer_cwmetrics/10resources_10records_10metrics-16     3.795k ± 3%   4.729k ± 1%  +24.63% (p=0.002 n=6)
MetricsConsumer_cwmetrics/10resources_100records_1metrics-16     3.281k ± 0%   6.161k ± 0%  +87.78% (p=0.002 n=6)
MetricsConsumer_cwmetrics/10resources_100records_10metrics-16    28.02k ± 0%   46.90k ± 0%  +67.39% (p=0.002 n=6)
geomean                                                          3.098k        3.722k       +20.16%

Documentation

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